Rotary drum brakes are commonly used in motor vehicles, from everyday passenger cars to trucks and large off-road industrial vehicles. A rotary drum brake mechanism has two major frictionally cooperating parts; a rotary drum which is typically affixed to the vehicle wheel and a pair of brake shoes mounted on a support plate carried by the vehicle's suspension. In order to brake a wheel and the associated brake drum, the brake shoes are shifted by an actuator relative to the support plate to cause the frictional surface on the outer periphery of the brake shoes to engage the cylindrical surface of the brake drum. The resulting braking force is transmitted through the brake shoes to the vehicle suspension via the support plate, "spider", carrying the brake shoes.
As a result of wear, it is necessary to periodically replace the brake shoes and/or the frictional material provided thereon. Due to the large number of brake shoes typically required in a motor vehicle, and as a result of the necessity to periodically replace or rebuild brake shoes, it is highly desirable to minimize the cost of brake shoe assembly. Due to the safety aspects of the brake, enhanced reliability is also very desirable. Brake shoes, however, are required to provide a very strong structure having precisely defined surfaces for mounting the brake shoes on the plate and the associated brake actuator.
Brakes shoes are typically formed in generally symmetrical pairs, with each shoe having a semi-cylindrical outer surface covered with a friction material. The friction material is typically mounted on a table member metal plate formed into a semi-cylindrical shape generally corresponding to the contour of the associated brake drum. Radially inboard and securely affixed to the table member is one or more web members, typically a stamped steel plate forming an arcuate segment having a pair of ends. The ends of the brake shoe webs cooperate with the brake actuator and a stationary support pin affixed to the support plate enabling the brake actuator to simultaneously bias the two brake shoes into engagement with the brake drum when desired.
In the case of heavy duty brake shoes, the manufacturing process involves the attachment of web and table members by means of a high energy joining process. This process (typically welding) produces considerable distortion of the web and table members, due to the heat involved in the welding process. To mitigate this distortion, which is deleterious to the function of the brake, it is necessary to perform a re-strike (coining) operation to the shoe. This process reforms the cylindrical outer surface of the shoe. However, this process also changes the location of the shoe web first and second ends that are used in operation of the brake. Therefore, it is necessary to machine the shoe web first and second ends to create accurate location points relative to the outer surface of the shoe. Additionally, in conventional processes, it is commonly necessary to machine these ends to create a finished surface as the rough edged web stampings are not adequate for this purpose.
It is the primary object of this invention to minimize or eliminate the need for post assembly processing of the brake shoe assembly, thereby reducing the total cost of manufacturing said shoes. It is also the intent of this invention to improve the reliability and durability of the shoe which will add value to the end user of the brake shoe.